I need help i'm worried about my girlfriends health. Please Help?

My girlfriends mother keeps commenting on her weight and she doesn't like it, even though I think she's perfect in every way!! Her mom makes her take this pill and she doesn't want to eat anything after she takes the pill. This leaves me in a situation where my girlfriend is feeling very unwell and I can't do much about it! I am extremely concerned for her health and I'm getting worried!